The process of construction can vary significantly depending on the scope of the project and the particulars of the structure. Construction processes can be categorized as residential, industrial, commercial, or civil to name a few. Many construction processes have a basic life cycle that includes design, planning (preconstruction), building (construction), and operation and maintenance (O&M). During the design phase, 3D models or 2D layouts and cross-sections are created to represent the end product. The end product, also referred to as product, is the building, bridge, airport or other structure that needs to be built or reconstructed. Once the designs (e.g., architectural, structural, mechanical) are completed, the building process shifts to the preconstruction and construction phases where managing the project can be critical. Project management may include activities such as purchasing materials, hiring work crews, finalizing required tasks, and creating schedules (i.e. specifying the start and end times of construction tasks, effectively ordering the tasks to maximize efficiency). Once the product is built, the final phase of the project lifecycle process can include maintenance and building operations.
The so called critical path method (CPM) is a project management technique used for creating schedules. The basic steps of CPM include creating a list of all the required tasks, including the duration of time allocated to complete the task, and identifying task dependencies (i.e. situation where a task cannot start until its predecessor tasks are completed). Using the list of tasks, their durations, and predecessors, CPM determines the shortest time to complete the project not taking into account space and resource requirements. Further, CPM visually presents the earliest and latest time that a task can start and finish (without accounting for specific space and resource requirements) without increasing the duration of the project. CPM identifies critical tasks (tasks that cannot be delayed without delaying the project's duration) and so called floats (tasks that can be delayed without extending the project's duration). A critical path is determined by chronologically ordering the critical tasks. In many instances, construction tasks can be performed in parallel provided work crews are not operating in the same space in such a way that they will interfere with each other. Therefore, an important aspect of scheduling tasks can be attempting to avoid conflicting needs for access to space within a construction site.
Another technique used in scheduling is the so called line of balance (LOB) method. The LOB method includes creating a chart with time (traditionally calendar days in sequential order) along the top and location or zones of the construction site along on the left hand side. A line representing a particular task is sketched starting from the bottom left of the chart progressing upwards from zone to zone and to the right (passage of time). By observing points on the line, a project manager can know the zone and time that a task is to be performed in. Multiple lines representing multiple tasks are placed on the chart to simultaneously visualize the location and time that tasks are progressing along the construction process. The LOB method is useful for predicting lag time between two separate works.
Building Information Models are 3D object oriented models that include information about the product such as the architectural elements, the material they are made of, locations and other information. Linking a 3D model, such as Building Information Model (BIM), to a schedule results in a 4D model. A 4D model is an animated step-by-step visualization of the progression of the construction process in a series of sequential events. Therefore 4D models are another tool that can be used in project management.